Is it possible to measure the groung rod resistance with a normal meter say fluke 87 or 175? If so how do you take the measurement.

The only way I've known of testing ground rods without a ground-testing meter, is to disconnect the EGC, place a 5A cartridge fuse in line with the EGC and a 120V line, turn on the power *briefly*, and if the fuse blows, you're done, if it don't, then drive another rod. Gives you a "threshold" of 24 Ohms, rather than the NEC 25, but it works. If you've got (closer to) 125V (we do here in Greenbrier County) then it's a perfect 25 Ohms.

Plus, you can gather nightcrawlers after the test!

I also read this in (I think) an older version of the American Electrician's Handbook (say, 1970's?)...

Kids, don't try this at home!

I think I'll go gather some worms and find that fishing hole Joe took a picture of
Now where did I put that" 5amp worm gatherin tool "

'66wv—That’s a very interesting proposal. What would be considered a proper waiting period for fuse operation? Any difference for time-delay type versus less-expensive one time?

Reel-Break:
Most contractors in our area just drive 2 rods from the get-go. Most AHJ's require documentation of the 25 ohms or less, and a meter to test and print results is pricey. Rods are cheap, and driving them with a roto hammer is quick.

66 thats a test to remember, I'll pass it on to my guys. Do you need "documentation" for your AHJ's or???

John

Hee hee...

I've never tried this method, just read about it once and found it to be intriguing!

PoCo wants two rods here, period. No fun!



To further ReelBreak's Q, what minumum voltage and sensitivity must a meter operate at to be useful for ground rod resistance testing?

My DMM (Fluke T-5 1000) will easily meter 25 Ohms, why won't it work on rods?



[This message has been edited by sparky66wv (edited 10-10-2002).]

66
the reason we can't use our flukes to do this is because we don't know exactly where to stick the other probe into the earth. this is why biddle can get a grand for these instructions supplied with their meters.
watt

There is a very reasonably priced tester available in the store here.

As far as paying big bucks for instructions, save your money and go here, http://www.tradeport.on.ca/ApplicationNotes/aemc.pdf

This is almost identicle to Biddle's instructions, and a little more detailed.

Roger

Could we check resistance from the opened EGC to the neutral? Wouldn't we be testing for continuiuty for any and all grounding electrodes attached to the grounded conductor?

How about to the nearest PoCo rod?

A ground resistance tester uses three electrodes, one is a reference electrode. A fluke DMM just won't work.

When I was working for the Ground Electronics Engineering and Installation Agency in the US Air Force the engineers would use a signal generator and two good meters connected to the ground under test and two separate test rods. The test rods were cut down sectional rods that could have a treaded pipe T and two nipples as a withdrawal handle. You ran the test recorded the current to the 100 foot rod and the voltage at the 62 foot rod and applied the results to a graph. The slope method is laid out in several different publications but I don't know of any that are on line. The reason that you cannot use the 120 volts as your power source is that stray currents present in the earth will throw the reading off. It was a fair amount of work to test that way and it was only done on remote sights when they needed a value and a null balance ground impedance meter was not available. Null Balance ground impedance testers were the state of the art in 1970.
--
Tom

[This message has been edited by tdhorne (edited 10-13-2002).]

John,

Most guys here in northern NJ just drive the 2 ground rods. I have had several EC's who just drove in 1 ground rod. If they did though, they left me a reading from a grounding type tester stating that there was 25 ohms or less to ground. Some of the grounding testers do use paper print outs.

Harold:
Yes, we accept the readings from a ground test on the EC's letterhead. It should have some details; meter used, date, readings, test locations, etc.
John

PS: Still think IMHO, it's easier to drive two rods; case closed.